Refrigerating device

ABSTRACT

A refrigerating device has a refrigerant circuit having a compressor ( 1 ), an indoor heat exchanger ( 3 ), a main motor operated valve (EV 1 ), and an indoor heat exchanger ( 5 ) connected in a loop, and uses, as a working medium, an R32 refrigerant or a mixed refrigerant containing R32 at at least 70 wt %. A supercooling heat exchanger ( 11 ) is disposed between the indoor heat exchanger ( 3 ) and the main motor operated valve (EV 1 ), and the liquid side of the refrigerant circuit are connected to the gas side by by-pass pipes ( 33, 34 ) through the supercooling heat exchanger ( 11 ). A supercooling motor operated valve (EV 2 ) is disposed at the by-pass pipe ( 33 ) upstream of the supercooling heat exchanger ( 11 ). A discharge temperature detected by a discharge temperature sensor ( 21 ) is determined by a discharge temperature determination part ( 10    b ), and based on the determination result, the opening of the supercooling motor operated valve (EV 2 ) is controlled so as to control an amount of the refrigerant flowing through the by-pass pipes ( 33, 34 ), whereby, using the working medium containing R32, the discharge temperature of the compressor is optimized without reducing the efficiency, and the COP and reliability are improved.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP00/07067 which has an Internationalfiling date of Oct. 12, 2000, which designated the United States ofAmerica.

TECHNICAL FIELD

The present invention relates to a refrigerating device using a workingmedium containing an R32 refrigerant (chemical formula: CH₂F₂) andparticularly to a refrigerating device which copes with a low GWP(global warming potential), is energy-saving and inexpensive, and iscapable of protecting the ozone layer and achieving recycling.

BACKGROUND ART

Hitherto, a refrigerating device of the heat pump type using a HCFC(hydrochlorofluorocarbon) refrigerant is known. The refrigerating devicehas a refrigerant circuit having a compressor, a condenser, a motoroperated valve, and an evaporator connected sequentially in the shape ofa loop and has a supercooling heat exchanger disposed between thecondenser and the motor operated valve. A gas refrigerant from thesupercooling heat exchanger is returned to a liquid injection of thecompressor and the suction side of the compressor. However therefrigerating device has a problem of deterioration of the COP(coefficient of performance) owing to decrease in the circulation amountof the refrigerant caused by by-passing of the refrigerant. The HCFCrefrigerants have a problem of deteriorating the environment of theearth because they have a high ozone-layer destruction coefficient and ahigh GWP (global warming potential).

Thus it is conceivable to use the R32 refrigerant as a low-GWP HFCrefrigerant capable of realizing a high COP without destroying the ozonelayer. However in its physical properties, the R32 refrigerant has ahigher discharge temperature than the HCFC refrigerants. Thus the R32refrigerant has a problem that it deteriorates oil for the refrigeratingdevice so that the reliability deteriorates.

In a conventional apparatus using R22, when a dryness of the refrigerantat the suction side of a high-pressure dome type compressor is 0.97, thedischarge temperature reaches 90° C. In the case of a low-pressure dometype compressor, when a dryness of the refrigerant at its suction sideis 0.97, the discharge temperature reaches 70° C.

The R32 refrigerant has a low pressure loss and its COP (coefficient ofperformance) can be improved, whereas in its physical properties, itsdischarge temperature rises to a temperature higher than the dischargetemperatures of R22, R410, and R407 by 15° C. in theory and by 10-15° C.in actual measurement. Thus in an apparatus using R22, R410 or R407,merely replacing such a refrigerant with R32 and changing therefrigeration oil to an oil compatible with R32 would lead to a problemof deterioration in reliability and performance.

Regarding the reliability, there is a fear that when the compressor isheated to a high temperature, deterioration of a material and oilproceeds and its long-term reliability deteriorates. In particular,because a compressor motor deteriorates (the demagnetizing forcedecreases) greatly owing to temperature, attention should be paid to aDC motor in dependence on a material that is used therefor.

Regarding the performance, supposing that the discharge-pipetemperature, the manner of controlling the refrigerant by using sensors,and the manner of controlling electric current are same as before, theR32 refrigerant has a problem of deteriorating the performance of therefrigerating device and reducing its operation area.

DISCLOSURE OF THE INVENTION

Therefore, it is an object of the present invention to provide arefrigerating device capable of optimizing the discharge temperature ofa compressor without deteriorating the efficiency of the compressor byusing a working medium containing an R32 refrigerant, so that the COPand reliability of the refrigerating device is improved.

In order to accomplish the above object, a refrigerating deviceaccording to the present invention comprises:

a refrigerant circuit having a compressor, a condenser, a mainpressure-reducing means, and an evaporator connected in a loop;

a supercooling heat exchanger disposed between the condenser and themain pressure-reducing means;

a by-pass pipe by which a gas side of the refrigerant circuit and aliquid side thereof are connected through the supercooling heatexchanger; and

a supercooling pressure-reducing means disposed at the by-pass pipeupstream of the supercooling heat exchanger, wherein:

the refrigerating device uses an R32 refrigerant or a mixed refrigerantcontaining the R32 refrigerant at at least 70 wt %; and

the refrigerating device further comprises:

a discharge temperature sensor detecting a discharge temperature of thecompressor;

a discharge temperature determination part determining the dischargetemperature detected by the discharge temperature sensor; and

a control part controlling the supercooling pressure-reducing means,based on a result of determination made by the discharge temperaturedetermination part, to control an amount of the refrigerant flowingthrough the by-pass pipe.

According to the refrigerating device, after the R32 refrigerant (or themixed refrigerant containing R32 at at least 70 wt %) discharged fromthe compressor is condensed by the condenser, the refrigerant ispressure-reduced by the main pressure-reducing means. Then therefrigerant vaporizes in the evaporator and returns to the suction sideof the compressor. At this time, the refrigerant pressure-reduced by thesupercooling pressure-reducing means flow from the liquid side of therefrigerant circuit to the gas side thereof at the downstream side ofthe evaporator by the by-pass pipe through the supercooling heatexchanger. The supercooling heat exchanger supercools the refrigerantflowing from the condenser to the main pressure-reducing means. Thedischarge temperature determination part determines the dischargetemperature detected by the discharge temperature sensor. Based on theresult of the determination, the control parts controls the supercoolingpressure-reducing means to adjust the amount of the refrigerant flowingthrough the by-pass pipes to a large amount or a small amount, accordingas the discharge temperature is high or low. Thus, when the dischargetemperature is high, the discharge temperature can be decreased byincreasing the amount of the refrigerant flowing through the by-passpipes. Accordingly, even if the R32 refrigerant (or the mixedrefrigerant containing R32 at at least 70 wt %) which is higher, due toits physical property, in the discharge temperature than the HCFCrefrigerants is used, it is possible to optimize the dischargetemperature without deteriorating the efficiency and thus improve theCOP and the reliability. A motor operated valve may be used as thesupercooling pressure-reducing means. Then, the opening of the motoroperated valve is controlled to control a by-pass refrigerant amount.Further a solenoid operated valve and a capillary may be combined toprovide the supercooling pressure-reducing means to control the by-passrefrigerant amount by opening and closing of the solenoid operatedvalve.

In one embodiment, when the discharge temperature determination partdetermines that the discharge temperature exceeds a set upper-limitvalue, the control part controls the supercooling pressure-reducingmeans to increase the amount of the refrigerant flowing through theby-pass pipe, and to decrease the amount of the refrigerant flowingthrough the by-pass pipe when the discharge temperature determinationpart determines that the discharge temperature is smaller than a setlower-limit value.

According to the refrigerating device, when the discharge temperaturedetermination part determines that the discharge temperature exceeds aset upper-limit value, the control part controls the supercoolingpressure-reducing means to increase the amount of the refrigerantflowing through the by-pass pipe. On the other hand, when the dischargetemperature determination part determines that the discharge temperatureis smaller than the set lower-limit value, the control part controls thesupercooling pressure-reducing means to decrease the amount of therefrigerant flowing through the by-pass pipe. Thereby optimum control ofthe discharge temperature can be accomplished without deteriorating theefficiency.

In another embodiment, the supercooling pressure-reducing meanscomprises a supercooling motor operated valve, and the refrigeratingdevice further comprises a condensation temperature sensor detecting acondensation temperature of the condenser; an evaporation temperaturesensor detecting an evaporation temperature of the evaporator; and atarget discharge temperature computing part computing a target dischargetemperature, based on the condensation temperature detected by thecondensation temperature sensor, the evaporation temperature detected bythe evaporation temperature sensor, and an opening of the supercoolingmotor operated valve. The control part controls the mainpressure-reducing means to allow the discharge temperature of thecompressor to attain to the target discharge temperature.

According to the refrigerating device, based on the condensationtemperature of the condenser detected by the condensation temperaturesensor, the evaporation temperature of the evaporator detected by theevaporation temperature sensor, and the opening of the supercoolingmotor operated valve, the target discharge temperature computing partcomputes the target discharge temperature suitable to the operationconditions or situation (cooling operation/heating operation, operationfrequency of the compressor, etc.). Based on the target dischargetemperature computed by the target discharge temperature computing part,the control part controls the main pressure-reducing means to controlthe amount of the refrigerant flowing through the refrigerant circuit sothat the discharge temperature of the compressor attains to the targetdischarge temperature. Thus, optimum control of the dischargetemperature can be accomplished according to the amount of therefrigerant flowing through the by-pass pipe, namely, a supercoolingdegree.

In one embodiment, the refrigerating device further comprises anevaporator-exit temperature sensor detecting a temperature at an exit ofthe evaporator. The control part controls the main pressure-reducingmeans and the supercooling motor operated valve, based on the targetdischarge temperature computed by the target discharge temperaturecomputing part and the temperature at the exit of the evaporatordetected by the evaporator-exit temperature sensor.

According to the refrigerating device, the evaporator-exit temperaturesensor detects the temperature at the exit of the evaporator. Based onthe target discharge temperature computed by the target dischargetemperature computing part and the temperature at the exit of theevaporator detected by the evaporator-exit temperature sensor, thecontrol part controls the main pressure-reducing means and thesupercooling pressure-reducing means. By using the temperature at theexit of the evaporator to control the discharge temperature of thecompressor, it is possible to improve controllability of the amount ofthe refrigerant flowing through the by-pass pipe, namely,controllability of the supercooling degree.

Generally, as shown with a P-H (pressure-enthalpy) diagram in FIG. 12, amaximum temperature in a refrigerating cycle is a temperature at thedischarge side of the compressor.

The present inventors ascertained in experiments that when the R32refrigerant is used, the reliability of the compressor is ensured, eventhough a superheat SH is decreased to increase the wetness of the R32refrigerant, as shown with a P-H (Td3-Tcu3) line of FIG. 13, as comparedwith a conventional (Td1-Tcu1) line. As shown in FIG. 13, when thewetness of the R32 refrigerant at the suction side of the compressor isincreased, a temperature Td at the discharge side of the compressordecreases from Td1 to Td3. Thus it is possible to avoid reduction in thereliability and the performance.

Let the wetness be x, the refrigerant is in a complete gaseous statewhen x=1.0, in a liquid state when x=0, and in a fluidized state, or astate of two phases, when x=0.5, 0.6, 0.9, and so on. Supposing that thedryness is y, y=1−x.

As shown in test results of reliability of FIG. 11, in the case wherethe conventional R22 refrigerant was used, the reliability of thecompressor was at an unusable level unless the dryness thereof at thesuction side of the compressor was 0.90 or more. In the case of the R32refrigerant, it was confirmed in experiments that when the drynessthereof at the suction side of the compressor was not less than 0.60,the reliability of the compressor was at a usable level.

Accordingly, in one embodiment, a compressor sucks and compresses an R32refrigerant having a dryness of 0.65 or more or a mixed refrigerantcontaining R32 at at least 70 wt % and having a dryness of 0.65 or more.

In the embodiment, the compressor sucks and compresses the R32refrigerant having the dryness of 0.65 or more. Thus, as is apparentfrom the test results shown in FIG. 11, it is possible to use the R32refrigerant without deteriorating the reliability of the compressor andrealize energy-saving and a low GWP without reducing the reliability andperformance. Also in the case where the compressor sucks the mixedrefrigerant containing R32 at 70 wt % or more and having the dryness of0.65 or more as well, similar effects can be obtained.

In another embodiment, a compressor sucks and compresses an R32refrigerant having a dryness of 0.70 or more or a mixed refrigerantcontaining R32 at at least 70 wt % and having a dryness of 0.70 or more.

In the embodiment, since the compressor sucks the R32 refrigerant havingthe dryness of 0.70 or more, the reliability of the compressor can befurther improved. In the case where the compressor sucks the mixedrefrigerant containing R32 at at least 70 wt % and having the dryness of0.70 or more, similar effects can be obtained.

That is, a mixed refrigerant containing R32 at at least 70 wt % providesa pseudo-azeotropy, which allows the R32 refrigerant to have advantages(energy-saving and low GWP) over the R22 refrigerant.

In one embodiment, a compressor sucks and compresses an R32 refrigeranthaving a dryness of 0.75 or more or a mixed refrigerant containing R32at at least 70 wt % and having a dryness of 0.75 or more.

In the embodiment, since the compressor sucks the R32 refrigerant havingthe dryness of 0.75 or more, the reliability of the compressor can beenhanced to a maximum level as is apparent from the test results shownin FIG. 11. In the case where the compressor sucks the mixed refrigerantcontaining R32 at at least 70 wt % and having the dryness of 0.75 ormore as well, similar effects can be obtained.

In one embodiment, the refrigerating device comprises a control meansdetecting a discharge-pipe temperature of the compressor and controllingthe dryness of the refrigerant sucked by the compressor based on thedetected discharge-pipe temperature.

In the embodiment, the dryness of the refrigerant sucked by thecompressor is controlled based on the discharge-pipe temperature of thecompressor. Thus the dryness can be controlled by the simple controlmeans.

In one embodiment, the refrigerating device comprises a control meansdetecting a superheat and controlling the dryness of the refrigerantsucked by the compressor based on the detected superheat.

In the embodiment, the dryness of the refrigerant sucked by thecompressor is controlled based on the superheat. Thus, the dryness ofthe suction side can be controlled with high precision and thereliability of the compressor can be improved.

In another embodiment, the refrigerating device comprises a controlmeans detecting a subcooling degree and controlling the dryness of therefrigerant sucked by the compressor based on the detected subcoolingdegree. In the embodiment, the dryness of the refrigerant sucked by thecompressor is controlled based on the subcooling degree. Thus thedryness at the suction side can be controlled with high precision andthe reliability of the compressor can be improved.

In one embodiment, the refrigerating device comprises a control meanscontrolling a superheating degree at an exit of an evaporator. In theembodiment, the superheating degree at the exit of the evaporator iscontrolled to increase the wetness at the exit of the evaporator. Thusit is possible to prevent condensation on a fan rotor of the evaporator(in an indoor unit).

In another embodiment, a compressor is of a high-pressure dome type, andin a heating operation at a low temperature (for example, the outdoortemperature is −5° C. or below), the compressor sucks and compresses anR32 refrigerant having a dryness of 0.68 or more or a mixed refrigerantcontaining R32 at at least 70 wt % and having a dryness of 0.68 or more;and a discharge temperature of the compressor is set to 80-90° C.

In the embodiment, the dryness of the R32 refrigerant at the suctionside of the high-pressure dome type compressor is set to 0.68 or more,and the discharge temperature is set to 80-90° C. Thus it is possible touse the R32 refrigerant without deteriorating the reliability of thecompressor, which realizes energy-saving and a low GWP and avoidsdeterioration of the reliability and performance.

In one embodiment, a compressor is of a low-pressure dome type, and in aheating operation at a low temperature (for example, the outdoortemperature is −5° C. or below), the compressor sucks and compresses anR32 refrigerant having a dryness of 0.65 or more or a mixed refrigerantcontaining R32 at at least 70 wt % and having a dryness of 0.65 or more;and a discharge temperature of the compressor is set to 60-70° C.

In the embodiment, the dryness of the R32 refrigerant at the suctionside of the low-pressure dome type compressor is set to 0.65 or more,and the discharge temperature is set to 60-70° C. Thus it is possible touse the R32 refrigerant without deteriorating the reliability of thecompressor, which realizes energy-saving and a low GWP and avoidsdeterioration of the reliability and performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of an air conditioner, of heat pump type,serving as a refrigerating device of a first embodiment of the presentinvention;

FIG. 2 is a flowchart for describing the operation of a control deviceof the air conditioner;

FIG. 3 is a Mollier diagram of the air conditioner;

FIG. 4 is a circuit diagram of an air conditioner of a second embodimentof the present invention;

FIG. 5 is a flowchart for describing the operation of a control deviceof the air conditioner;

FIG. 6 is a circuit diagram of an air conditioner not having a bridgecircuit;

FIG. 7 is a circuit diagram of an air conditioner using a solenoidoperated valve and a capillary as a supercooling pressure-reducingmeans;

FIG. 8 is a circuit diagram of an air conditioner using an injectioncircuit;

FIG. 9 is a refrigerant circuit of an air conditioner which is anembodiment of the refrigerating device of the present invention;

FIG. 10 is a flowchart for describing the operation of a control deviceof the embodiment;

FIG. 11 is a chart showing results of a test for evaluating reliabilityof a compressor for each dryness of a refrigerant;

FIG. 12 shows an example of a Mollier diagram in an actual refrigeratingdevice; and

FIG. 13 shows a superheat SH and a sub-cooling degree SC in the Mollierdiagram.

BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the air conditioner of the present invention will bedescribed in detail below.

First Embodiment

FIG. 1 is a circuit diagram showing a schematic construction of a heatpump type air conditioner as a first embodiment of the refrigeratingdevice of the present invention. Reference numeral 1 denotes acompressor, 2 denotes a four-way selector valve connected to a dischargeside of the compressor 1, 3 denotes an outdoor heat exchanger whose oneend is connected to the four-way selector valve 2, 4 denotes a bridgecircuit serving as a rectifying means, 5 denotes an indoor heatexchanger, 6 denotes an accumulator 6 connected to the indoor heatexchanger 5 through the four-way selector valve 2.

The bridge circuit 4 has check valves 4A, 4B, 4C, and 4D permitting theflow of a refrigerant in only one direction, two input/output ports, oneinput port, and one output port. The outdoor heat exchanger 3 isconnected to one of the input/output ports of the bridge circuit 4. Theindoor heat exchanger 5 is connected to the other input/output port ofthe bridge circuit 4. The check valve 4A is connected to the oneinput/output port in a direction in which the flow of the refrigerantfrom the outdoor heat exchanger 3 is permitted. The check valve 4B isconnected to the other input/output port in a direction in which theflow of the refrigerant from the indoor heat exchanger 5 is permitted.The check valves 4A and 4B are connected to the output port, with bothvalves facing each other. The check valve 4C is connected to theinput/output port, to which the check valve 4B is connected, in thedirection in which the refrigerant to the indoor heat exchanger 5 ispermitted to flow. The check valve 4D is connected to the input/outputport, to which the check valve 4A is connected, in the direction inwhich the refrigerant to the outdoor heat exchanger 3 is permitted toflow. The check valves 4C and 4D are connected to the input port, withboth valves facing each other.

One end of a pipe 31 is connected to the output port of the bridgecircuit 4. The other end of the pipe 31 is connected to one end of anouter tube 11 a of a supercooling heat exchanger 11. One end of a pipe32 is connected to the input port of the bridge circuit 4. The other endof the pipe 32 is connected to the other end of the outer tube 11 a ofthe supercooling heat exchanger 11. A main motor operated valve EV1serving as a main pressure reduction means is disposed on the pipe 32.The pipe 31 is connected to one end of an inner tube 11 a of thesupercooling heat exchanger 11 through a by-pass pipe 33 on which aby-pass motor operated valve EV2 serving as a supercoolingpressure-reducing means is disposed. The other end of the inner tube 11b of the supercooling heat exchanger 11 is connected to a positionbetween the four-way selector valve 2 and the accumulator 6 through aby-pass pipe 34. As a result, in whichever direction the refrigerantflows between the outdoor heat exchanger 3 and the indoor heat exchanger5 by a change-over from a cooling operation to a heating operation orvice versa, the bridge circuit 4 allows the refrigerant to flow in onlythe direction from the supercooling heat exchanger 11 to the main motoroperated valve EV1.

A refrigerant circuit is constructed of the compressor 1, the four-wayselector valve 2, the outdoor heat exchanger 3, the main motor operatedvalve EV1, the indoor heat exchanger 5, and the accumulator 6. An R32refrigerant is used as a working medium.

The air conditioner has a discharge temperature sensor 21 detecting thedischarge temperature of the discharge side of the compressor 1, atemperature sensor 22 provided on the outdoor heat exchanger 3 andserving as a condensation temperature sensor or an evaporationtemperature sensor for detecting the refrigerant temperature of theoutdoor heat exchanger 3, a temperature sensor 23 provided on the indoorheat exchanger 5 and serving as an evaporation temperature sensor or acondensation temperature sensor for detecting the refrigeranttemperature of the indoor heat exchanger 5, and a control section 10controlling the cooling operation and the heating operation upon receiptof signals from each of the temperature sensors 22, 23, and 24. Thecontrol section 10 is constructed of a microcomputer, an input/outputcircuit, and the like, and has a control part 10 a controlling thecompressor 1, the main motor operated valve EV1, and the by-pass motoroperated valve EV2, a discharge temperature determination part 10 bdetermining the discharge temperature detected by the temperature sensor21, and a target discharge temperature computing part 10 c computing atarget discharge temperature, based on the discharge temperature, acondensation temperature, and an evaporation temperature detected by thetemperature sensors 21-23.

In the case where the air conditioner having the construction performsthe cooling operation, the compressor 1 is actuated with the four-wayselector valve 2 switched to a position shown with a solid line. As aresult, the refrigerant, having a high temperature and a high pressure,discharged from the compressor 1 flows through the four-way selectorvalve 2, the outdoor heat exchanger 3, the check valve 4A of the bridgecircuit 4, the supercooling heat exchanger 11, and to the motor operatedvalve EV1. The refrigerant pressure-reduced by the motor operated valveEV1 flows through the check valve 4D of the bridge circuit 4, the indoorheat exchanger 5, and to the four-way selector valve 2 and returns tothe accumulator 6 from the four-way selector valve 2. At this time, thesupercooling heat exchanger 11 supercools the refrigerant flowing intothe motor operated valve EV1, and in the indoor heat exchanger 5functioning as an evaporator, a liquid refrigerant having a lowtemperature and a low pressure vaporizes and is then exhausted from anexit side thereof.

When the air conditioner performs the heating operation, the compressor1 is actuated with the four-way selector valve 2 switched to a positionshown with a broken line. As a result, the refrigerant, having a hightemperature and a high pressure, discharged from the compressor 1 flowsthrough the four-way selector valve 2, the indoor heat exchanger 5, thecheck valve 4B, the supercooling heat exchanger 11, and the motoroperated valve EV1. The refrigerant pressure-reduced by the motoroperated valve EV1 flows through the check valve 4C of the bridgecircuit 4, the outdoor heat exchanger 3, and to the four-way selectorvalve 2 and returns to the accumulator 6 from the four-way selectorvalve 2. At this time, a high-temperature and high-pressure liquidrefrigerant upstream of the supercooling heat exchanger 11 is expandedby the by-pass motor operated valve EV2 and becomes a gaseousrefrigerant having a low temperature and a low pressure, which flowsinto the supercooling heat exchanger 11, and supercools the refrigerantflowing into the motor operated valve EV1.

As described above, in the cooling operation and the heating operation,owing to the provision of the bridge circuit 4, the supercooling heatexchanger 11 is disposed at the upstream side of the motor operatedvalve EV1 so that the supercooling heat exchanger 11 increasinglysupercools the refrigerant flowing into the motor operated valve EV1.The operation efficiency can be thereby improved.

The operation of the control section 10 will be described below withreference to the flowchart of FIG. 2. The cooling operation will be onlydescribed with reference to FIG. 2. In the heating operation, a changeis done between the condenser and the evaporator, and hence between thetemperature sensor 22 detecting the condensation temperature Tc and thetemperature sensor 23 detecting the evaporation temperature Te, and aprocessing similar to the cooling operation is executed.

With reference to FIG. 2, once the cooling operation starts, a dischargetemperature, Td, a condensation temperature, Tc, and an evaporationtemperature, Te are detected at step S1. That is, the temperature sensor21 detects the discharge temperature, Td, at the discharge side of thecompressor 1, and the temperature sensor 22 detects the condensationtemperature, Tc, of the outdoor heat exchanger 3 serving as thecondenser, and the evaporation temperature, Te, of the indoor heatexchanger 5 serving as the evaporator is detected.

Then the program goes to step S2 at which the discharge temperaturedetermination part 10 b of the control device 10 determines whether thedischarge temperature, Td, is more than a set upper-limit value. If itis determined that the discharge temperature, Td, is more than the setupper-limit value, the program goes to step S3 at which the motoroperated by-pass valve EV2 is opened at a predetermined opening. Thenthe program goes to step S4.

On the other hand, if it is determined that the discharge temperature,Td, is not more than the set upper-limit value, the program goes to stepS11 at which the discharge temperature determination part 10 bdetermines whether the discharge temperature, Td, is smaller than a setlower-limit value. If the discharge temperature determination part 10 bdetermines that the discharge temperature, Td, is smaller than the setlower-limit value, the program goes to step S12. On the other hand, ifthe discharge temperature determination part 10 b determines that thedischarge temperature, Td, is not smaller than the set lower-limitvalue, the program goes to step S4.

At step S12, it is determined whether a by-pass operation is beingperformed. If it is determined that the by-pass operation is beingperformed, the program goes to step S13 at which the motor operatedby-pass valve EV2 is closed by a predetermined value from a currentopening. On the other hand, if it is determined that the by-passoperation is not being performed, the program goes to step S4.

Thereafter at step S4, the target discharge temperature computing part10 c computes the target discharge temperature, Tk. The target dischargetemperature, Tk, is computed on the basis of the condensationtemperature, Tc, and the evaporation temperature, Te, both detected atstep S1 and the opening of the by-pass motor operated valve EV2.

Then the program goes to step S5 at which it is determined whether thedischarge temperature Td detected at step S1 is more than the targetdischarge temperature, Tk. If it is determined that the dischargetemperature, Td, is more than the target discharge temperature, Tk, theprogram goes to step S6 at which the main motor operated valve EV1 isopened. On the other hand, if it is determined that the dischargetemperature, Td, is not more than the target discharge temperature, Tk,the program goes to step S7 at which the main motor operated valve EV1is closed.

FIG. 3 shows a Mollier diagram in which the axis of ordinates indicatesthe pressure P and the axis of abscissas indicates the enthalpy 1.Referring to FIG. 3, for comparison, the case where the supercoolingheat exchanger 11 is not provided (a by-pass is not provided) and thecase where the supercooling heat exchanger is provided (a by-pass isprovided) will be described below.

In the case where the supercooling heat exchanger 11 is not provided, anormal cycle changes as shown with a broken line in FIG. 3. On the otherhand, in the case where the supercooling heat exchanger 11 is provided,the refrigerant cycle changes as shown with a solid line (and a thickersolid line) of FIG. 3. That is, the refrigerant in a state A (exit ofevaporator) at the input side of the compressor 1 is changed into ahigh-pressure state B by the compressor 1, and owing to condensation ofthe refrigerant in the outdoor heat exchanger 3, the state B is changedinto a state C (branch) in which the refrigerant has a small enthalpy.The supercooling heat exchanger 11 supercools the refrigerant at theexit side of the outdoor heat exchanger 3 to change the state of therefrigerant from C to D.

Then the refrigerant supercooled by the supercooling heat exchanger 11is changed into a pressure reduced state E owing to expansion thereof atthe main motor operated valve EV1. The refrigerant in the state E ischanged into the state A in which the enthalpy has become high owing toheat absorption from outside air, with the pressure being approximatelyconstant due to the evaporation at the indoor heat exchanger 5. Then,the exit side of the indoor heat exchanger 5 and the exit side of theby-pass pipe of the supercooling heat exchanger 11 are joined with eachother to change the state from A to Y. As a result, the dischargetemperature of the compressor 1 decreases.

As described above, the discharge temperature Td detected by thedischarge temperature sensor 21 is discriminated or determined by thedischarge temperature determination part 10 b. Then, based on the resultof the determination, the supercooling motor operated valve EV2 iscontrolled to adjust the amount of the refrigerant flowing through theby-pass pipes 33 and 34 to a large amount or a small amount, accordingas the discharge temperature is high or low. Thereby when the dischargetemperature is high, the discharge temperature is decreased byincreasing the amount of the refrigerant flowing through the by-passpipes. Accordingly, even if the R32 refrigerant higher in the dischargetemperature than the HCFC refrigerants is used, it is possible tooptimize the discharge temperature of the compressor 1 withoutdeteriorating the efficiency and improve the COP and the reliability.

In accordance with the result of comparison, made by the dischargetemperature determination part 10 b, between the discharge temperatureand the set upper-limit value as well as the set lower-limit value, thecontrol part 10 a controls the supercooling motor operated valve EV2 toaccurately adjust the amount of the refrigerant flowing through theby-pass pipes 33 and 34, whereby an optimum control of the dischargetemperature can be accomplished.

The target discharge temperature computing part 10 c computes the targetdischarge temperature, Tk, suitable to the operation conditions orsituation (cooling operation/heating operation, operation frequency ofthe compressor, etc.), based on the condensation temperature, Tc, theevaporation temperature, Te, and the opening of the supercooling motoroperated valve EV2. Then, based on the obtained target dischargetemperature Tk, the control part 10 a controls the opening of the mainmotor operated valve EV1. The control of the main motor operated valvecombined with the control of the supercooling motor operated valve EV2makes it possible to accurately control the discharge temperature of thecompressor 1.

Second Embodiment

FIG. 4 is a circuit diagram showing a schematic construction of aheat-pump type air conditioner serving as a refrigerating device of asecond embodiment of the present invention. Except for temperaturesensors 24, 25 and the operation of the control device 10, the airconditioner of the second embodiment has the same construction as thatof the air conditioner of the first embodiment. Thus the sameconstituent parts of the air conditioner of the second embodiment asthose of the air conditioner of the first embodiment are denoted by thesame reference numerals and description thereof is omitted herein.

As shown in FIG. 4, the air conditioner has a temperature sensor 24disposed on the outdoor heat exchanger 3 and serving as anevaporator-exit temperature sensor and a temperature sensor 25 disposedon the indoor heat exchanger 5 and serving as an evaporator-exittemperature sensor. The temperature sensors 24 and 25 are installed onthe outdoor heat exchanger 3 and the indoor heat exchanger 5respectively in such a way that the temperature sensors 24 and 25 arepositioned within ⅓ of the entire length of the heat exchangers from thegas side thereof.

The control section 10 is constructed of a microcomputer, aninput/output circuit, etc. and has a control part 10 a controlling thecompressor 1, the main motor operated valve EV1, and the by-pass motoroperated valve EV2, a discharge temperature determination part 10 bcomparing a discharge temperature detected by the temperature sensor 21with a set upper-limit value and a set lower-limit value, a targetdischarge temperature computing part 10 c computing a target dischargetemperature, based on a discharge temperature, a condensationtemperature, and an evaporation temperature detected by the temperaturesensors 21-23, and a target evaporator-exit temperature computing part10 d computing a target evaporator-exit temperature, based on theevaporation temperature detected by the temperature sensor 22 or 23.

In the air conditioner having the construction, the operation of thecontrol section 10 is similar to that of the air conditioner in stepsS1-S4 and S11-S13 of the flowchart of FIG. 2 of the air conditioner ofthe first embodiment, but different from the air conditioner of thefirst embodiment in only steps S5-S7. FIG. 5 shows a flowchart of theoperation only in steps different from the air conditioner of the firstembodiment.

After the target discharge temperature, Tk, is computed at step S4 ofFIG. 2, an evaporator-exit temperature, Ts, is detected at step S21 ofFIG. 5. In this case, in the cooling operation, the temperature sensor25 detects the temperature of the refrigerant at the exit side of theindoor heat exchanger 5 serving as the evaporator. In the heatingoperation, the temperature sensor 24 detects the temperature of therefrigerant at the exit side of the outdoor heat exchanger 3 serving asthe evaporator.

Thereafter at step S22, the target evaporator-exit temperature computingpart 10 d computes a target evaporator-exit temperature, Tj. The targetevaporator-exit temperature, Tj, is found by using an equation shownbelow:

Tj=evaporation temperature Te+A

where A is determined by a table prepared in accordance with theoperation conditions for cooling/heating operation and the operationfrequency of the compressor.

Then at step S23, it is determined whether the discharge temperature,Td, is more than the target discharge temperature, Tk. If it isdetermined that the discharge temperature, Td, is more than the targetdischarge temperature, Tk, the program goes to step S24. On the otherhand, if it is determined that the discharge temperature, Td, is notmore than the target discharge temperature Tk, the program goes to stepS28.

Thereafter at step S24, it is determined whether the evaporator-exittemperature, Ts, is more than the target evaporator-exit temperature,Tj. If it is determined that the evaporator-exit temperature, Ts, ismore than the target evaporator-exit temperature, Tj, the program goesto step S25 at which according to an instruction of the control part 10a, the main motor operated valve EV1 is opened further by apredetermined amount from a current opening. On the other hand, if it isdetermined at step 24 that the evaporator-exit temperature, Ts, is notmore than the target evaporator-exit temperature, Tj, the program goesto step S26 at which according to an instruction of the control part 10a, the main motor operated valve EV1 is closed by a given amount fromthe current opening, and at step S27, the motor operated by-pass valveEV2 is opened further by a given amount from a current opening.Thereafter the program returns to step S1 of FIG. 2.

It is determined at step S28 whether the evaporator-exit temperature,Ts, is more than the target evaporator-exit temperature, Tj. If it isdetermined that the evaporator-exit temperature Ts is not more than thetarget evaporator-exit temperature, Tj, the program goes to step S29 atwhich according to an instruction of the control part 10 a, the mainmotor operated valve EV1 is closed by a given amount from the currentopening. On the other hand, if it is determined at step S28 that theevaporator-exit temperature, Ts, exceeds the target evaporator-exittemperature, Tj, the program goes to step S30 at which under the controlof the control part 10 a, the main motor operated valve EV1 is openedfurther from the current opening by a given amount and at step S31, themotor operated by-pass valve EV2 is closed by a given amount from thecurrent opening. Thereafter the program returns to step S1 of FIG. 2.

As is obvious from the above, the air conditioner has advantages similarto the advantages of the air conditioner of the first embodiment.Further, due to utilization of evaporator-exit temperature for thecontrol of the discharge temperature of the compressor 1, the airconditioner has improved controllability of the amount of therefrigerant flowing through the by-pass pipe, namely, improvedcontrollability of the supercooling degree.

Although the air conditioner has been described as the refrigeratingdevice in the first and second embodiments, the present invention isapplicable to other types of refrigerating devices.

Although the air conditioner using the R32 refrigerant has beendescribed in the first and second embodiments, the refrigerant used forthe refrigerating device is not limited to the R32 refrigerant, but amixed refrigerant containing R32 at at least 70 wt % may be usedtherefor. For example, it is possible to use a mixed refrigerant of theR32 refrigerant and CO₂, the content of R32 being from 70 wt % to 90 wt% inclusive, a mixed refrigerant of R32 and R22, the content of R32being from 70 wt % to 90 wt % inclusive, or the like.

In the first and second embodiment, the air conditioners having therefrigerant circuit and the supercooling circuit shown in FIGS. 1 and 4have been described as the refrigerating device. However theconstruction of the refrigerating device is not limited to the airconditioners shown in FIGS. 1 and 4. For example, a refrigerating devicehaving a construction as shown in FIG. 6 in which the bridge circuit isremoved from FIG. 1 may be used. In this case, the supercooling motoroperated valve EV2 is opened in only the heating operation to by-passthe refrigerant. Also, the refrigerating device may have a constructionas shown in FIG. 7 in which a solenoid operated valve 61 and a capillary62 are used as the supercooling pressure-reducing means instead of thesupercooling motor operated valve of FIG. 1. Further as shown in FIG. 8,the refrigerating device may have an injection circuit for injecting agas refrigerant from the supercooling heat exchanger 11 into anintermediate-pressure portion of a compressor 71 through a by-pass pipe35. In FIGS. 6 through 8, the same constituent parts as those shown inFIG. 1 are denoted by the reference numerals.

Third Embodiment

FIG. 9 shows a refrigerant circuit of an air conditioner being a thirdembodiment of the refrigerating device of the present invention. In thethird embodiment, the R32 refrigerant is used. The third embodiment hasa refrigerant circuit having a compressor 101, a four-way selector valve104, an outdoor heat exchanger 102, an expansion valve 103, a valve 126,an indoor heat exchanger 105, a valve 125, a gas-liquid separator 106,and an accumulator 107 sequentially connected. An outdoor unit 121having the outdoor heat exchanger 102 is connected to an indoor unit 122through a connection piping.

The third embodiment has a control section 108 provided by amicrocomputer. The control section 108 is connected to a temperaturesensor 113 mounted on a suction-side pipe of the compressor 101, atemperature sensor 112 mounted on a discharge-side pipe of thecompressor, a temperature sensor 117 mounted on the outdoor heatexchanger 102, a temperature sensor 115 mounted on the indoor heatexchanger 105, a temperature sensor 111 detecting an outdoortemperature, and a temperature sensor 116 detecting an indoortemperature.

The operation of the control section 108 of the third embodiment will bedescribed below with reference to FIG. 10. Initially at step S101, it isdetermined at step S101 whether the air conditioner uses the R32refrigerant. If it is determined that the air conditioner uses the R32refrigerant, the program goes to step S102. Whether the air conditioneruses the R32 refrigerant may be determined on the basis of informationinputted in advance. If it is determined that the air conditioner doesnot use the R32 refrigerant, the program goes to step S105 at which aconventional control is continuously executed. The “conventionalcontrol” means a control of the compressor 101 and the expansion valve103 based on a discharge-pipe temperature, Tdis, obtained from thetemperature sensor 112.

At step S102, it is determined whether the discharge-pipe temperature,Tdis, is equal to or higher than a predetermined value within the rangeof 135° C.-125° C. If it is determined that the discharge-pipetemperature, Tdis, is equal to or higher than the predetermined value,the program goes to step S103. On the other hand, if it is determinedthat the discharge-pipe temperature, Tdis, is less than thepredetermined value, the program goes to step S105.

At step S103, a superheat SH (see FIG. 13) is detected whereby thewetness of the refrigerant at the suction side of the compressor 101 isdetected. That is, the superheat SH which is the difference between atemperature, Tsuc, of the compressor 101 at its suction side obtainedfrom the temperature sensor 113 and the temperature of the evaporatorobtained from the temperature sensor 117 or 115 (temperature, Tin, ofthe indoor heat exchanger 105 in cooling operation) is detected. Then anoperation of increasing the number of rotations of the compressor 101and/or an operation of opening the expansion valve 103 is performed todecrease the superheat SH to thereby increase the wetness. Thereby therefrigerant temperature of the compressor at its discharge side isdecreased to avoid deterioration of the reliability and the performance.

Thereafter the program goes to step S104 at which it is determinedwhether the superheat SH is equal to or more than a predetermined valuewithin the range of 0.85-0.75. If it is determined that the superheat SHis equal to or more than the predetermined value, the program goes tostep S105 at which the conventional control is continuously executed.

On the other hand, if it is determined that the superheat SH is lessthan the predetermined value (overwet) within the range of 0.85-0.75,the program goes to step S106 at which the number of rotations of thecompressor 101 is decreased so that the circulation amount of therefrigerant is decreased. By thus doing, the superheat SH is increasedby a predetermined value and hence the wetness is decreased accordingly,whereby the dryness of the refrigerant is kept at a proper value(0.85-0.75).

Thereafter the program goes to step S107 at which the processing ofsteps S103 and S104 is executed to decrease the superheat by apredetermined value, and an operation of decreasing the discharge-pipetemperature is performed. If the superheat is less than the proper value(0.85-0.75), the program returns to step S106 at which the superheat isincreased. On the other hand, if it is determined at step S107 that thesuperheat is more than the proper value (0.85-0.75), the program returnsto step S108 at which the expansion valve 103 is throttled to decreasethe superheat and hence increase the wetness to thereby decrease thedischarge-pipe temperature, Tdis. Thereafter the program goes to stepS109.

At step S109, the operation of steps S103 and S104 is performed. Thatis, the discharge-pipe temperature is decreased by performing theoperation of decreasing the superheat SH. Then, the program goes to stepS105 if the superheat SH is equal to or larger than the predeterminedvalue (in the range of 0.85-0.75) at which sufficient reliability isobtained. If the superheat SH has not reached the predetermined value,the program goes to step S106 at which the superheat-increasingoperation is performed again.

As described above, in the third embodiment, when the discharge-pipetemperature becomes the predetermined value or more, the superheat SH isdecreased to increase the wetness and decrease the discharge-pipetemperature (steps S102, S103). Then if it is determined that thesuperheat SH is short, to increase the dryness, the number of rotationsof the compressor 101 is decreased to increase the superheat SH to aproper value (0.85-0.75) at which the reliability of the compressor 101is sufficiently secured.

Owing to the control, the discharge temperature can be decreased bydecreasing the dryness (superheat) of the R32 refrigerant, sucked by thecompressor 101, to fall within the range where the reliability of thecompressor 101 is sufficiently secured. Thus energy-saving and a low GWPis realized while avoiding reduction in the reliability (reduction inlubricity of compressor, wear, and the like) and in the performance (lowtemperature performance in the heating operation).

In the third embodiment, although the proper value of the dryness(superheat) is set to the range of 0.85-0.75, the proper value thereofmay be set to the range not less than 0.65, 0.70 or 0.75. In the thirdembodiment, although the compressor 101 and the expansion valve 103 arecontrolled based on the superheat, the compressor and the expansionvalve may be controlled based on the discharge-pipe temperature of thecompressor or a sub-cooling degree (SC). Although the refrigerantconsisting solely of R32 is used in the third embodiment, similareffects can be obtained even in the case where a mixed refrigerantcontaining R32 at at least 70 wt % is used.

That is, a mixed refrigerant containing R32 at at least 70 wt % providesa pseudo-azeotropy, which allows the R32 refrigerant to display itsadvantages (energy-saving and low GWP) over the R22 refrigerant.

Compressors include a high-pressure dome type compressors andlow-pressure dome type compressors. The “high-pressure dome type” is atype of a compressor wherein a compressor motor is placed in ahigh-pressure atmosphere of a discharge gas or the like, whereas the“low-pressure dome type” is a type of a compressor wherein a compressormotor is placed in a low-pressure atmosphere of a low-pressure gas or aliquid. The discharge temperature of the low-pressure dome typecompressor is lower by 15° C.-20° C. than that of the high-pressure dometype compressor. Accordingly in the case where the low-pressure dometype compressor is adopted in the air conditioner adopting the R32refrigerant, the dryness of the refrigerant sucked by the compressor isset to 0.65-0.95 to control the discharge temperature of the compressorto 60° C.-70° C. By thus doing, it is possible to realize anenergy-saving, low-GWP and low-cost air conditioner that avoidsdeterioration in the reliability and performance of the compressor.

In the third embodiment, the control part 108 may be so constructed asto control the superheating degree of the refrigerant at the exit of theindoor heat exchanger 105 serving as the evaporator to thereby increasethe wetness of the refrigerant at the exit of the indoor heat exchanger105 and prevent condensation on a fan rotor of the indoor heat exchanger105. The condensation prevention control may be applied to a case usinga mixed refrigerant containing 50 wt % R32 and 50 wt % R125 as well as acase using R407C (R32 /R125/R134a: 23/25/52 wt %).

What is claimed is:
 1. A refrigerating device comprising: a refrigerantcircuit having a compressor (1), a condenser (3, 5), a mainpressure-reducing means (EV1), and an evaporator (5, 3) connected in aloop; a supercooling heat exchanger (11) disposed between the condenser(3, 5) and the main pressure-reducing means (EV1); a by-pass pipe (33,34) by which a gas side of the refrigerant circuit and a liquid sidethereof are connected through the supercooling heat exchanger (11); anda supercooling pressure-reducing means disposed at the by-pass pipe (33,34) upstream of the supercooling heat exchanger (11), wherein: therefrigerating device uses an R32 refrigerant or a mixed refrigerantcontaining the R32 refrigerant at at least 70 wt %; and therefrigerating device further comprises: a discharge temperature sensor(21) detecting a discharge temperature of the compressor (1); adischarge temperature determination part (10 b) determining thedischarge temperature detected by the discharge temperature sensor (21);and a control part (10 a) controlling the supercooling pressure-reducingmeans, based on a result of determination made by the dischargetemperature determination part (10 b), to control an amount of therefrigerant flowing through the by-pass pipe.
 2. A refrigerating deviceaccording to claim 1, wherein when the discharge temperaturedetermination part (10 b) determines that the discharge temperatureexceeds a set upper-limit value, the control part (10 a) controls thesupercooling pressure-reducing means to increase the amount of therefrigerant flowing through the by-pass pipe (33, 34), and to decreasethe amount of the refrigerant flowing through the by-pass pipe (33, 34)when the discharge temperature determination part (10 b) determines thatthe discharge temperature is smaller than a set lower-limit value.
 3. Arefrigerating device according to claim 1, wherein the supercoolingpressure-reducing means comprises a supercooling motor operated valve(EV2), and the refrigerating device further comprises: a condensationtemperature sensor (22, 23) detecting a condensation temperature of thecondenser (3, 5); an evaporation temperature sensor (23, 22) detectingan evaporation temperature of the evaporator (5, 3); a target dischargetemperature computing part (10 c) computing a target dischargetemperature, based on the condensation temperature detected by thecondensation temperature sensor (22, 23), the evaporation temperaturedetected by the evaporation temperature sensor (23, 22), and an openingof the supercooling motor operated valve (EV2), the control part (10 a)controls the main pressure-reducing means (EV1) to allow the dischargetemperature of the compressor (1) to attain to the target dischargetemperature.
 4. A refrigerating device according to claim 3, furthercomprising an evaporator-exit temperature sensor (24, 25) detecting atemperature at an exit of the evaporator (3, 5), wherein the controlpart (10 a) controls the main pressure-reducing means (EV1) and thesupercooling motor operated valve (EV2), based on the target dischargetemperature computed by the target discharge temperature computing part(10 c) and the temperature at the exit of the evaporator detected by theevaporator-exit temperature sensor (24, 25).
 5. A refrigerating deviceof which a compressor (101) sucks and compresses an R32 refrigeranthaving a dryness of 0.65 or more or a mixed refrigerant containing R32at at least 70 wt % and having a dryness of 0.65 or more.
 6. Arefrigerating device according to claim 5, comprising a control means(108) detecting a discharge-pipe temperature of the compressor (101) andcontrolling the dryness of the refrigerant sucked by the compressorbased on the detected discharge-pipe temperature.
 7. A refrigeratingdevice according to claim 5, comprising a control means (108) detectinga superheat (SH) and controlling the dryness of the refrigerant suckedby the compressor-based on the detected superheat.
 8. A refrigeratingdevice according to claim 5, comprising a control means (108) detectinga subcooling degree (SC) and controlling the dryness of the refrigerantsucked by the compressor based on the detected subcooling degree.
 9. Arefrigerating device according to claim 5, comprising a control means(108) controlling a superheating degree at an exit of an evaporator(105, 102).
 10. A refrigerating device of which a compressor (101) sucksand compresses an R32 refrigerant having a dryness of 0.70 or more or amixed refrigerant containing R32 at at least 70 wt % and having adryness of 0.70 or more.
 11. A refrigerating device of which acompressor (101) sucks and compresses an R32 refrigerant having adryness of 0.75 or more or a mixed refrigerant containing R32 at atleast 70 wt % and having a dryness of 0.75 or more.
 12. A refrigeratingdevice of which a compressor is of a high-pressure dome type, andwherein the compressor sucks and compresses an R32 refrigerant having adryness of 0.68 or more or a mixed refrigerant containing R32 at atleast 70 wt % and having a dryness of 0.68 or more; and a dischargetemperature of the compressor is set to 80-90° C.
 13. A refrigeratingdevice of which a compressor is of a low-pressure dome type, and whereinthe compressor sucks and compresses an R32 refrigerant having a drynessof 0.65 or more or a mixed refrigerant containing R32 at at least 70 wt% and having a dryness of 0.65 or more; and a discharge temperature ofthe compressor is set to 60-70° C.